Branches, Connectors, and Nodes[LINK]
In EnergyPlus, the HVAC system and plant form a network (technically, a graph). The individual pieces of equipment – the fans, coils, chillers, etc. – are connected together by air ducts and fluid pipes. In EnergyPlus nomenclature, the air and fluid circuits are called loops. Specifying how an individual system and plant are connected is done in the EnergyPlus input (IDF) file. The overall structure of the network is defined with Branch and Connector objects. The detail is filled with components and their inlet and outlet nodes. A Branch consists of one or more components arranged sequentially along a pipe or duct. A Connector specifies how three or more branches are connected through a Splitter or Mixer. Nodes connect components along a branch: the outlet node of one component is the inlet node of the next downstream component. The nodes represent conditions at a point on a loop. Each component has one or more inlet and outlet nodes, depending on how many loops it interacts with. A fan, for instance, has one inlet node and one outlet node, since it interacts with a single air loop. A water coil will have 2 inlet and 2 outlet nodes, since it interacts with an air and a fluid loop. Figure 1 shows a diagram of an EnergyPlus HVAC input.
As an illustration of how such a network is built up on the IDF, here is the section of the IDF that describes the supply fan, splitter, and heating and cooling coil section of the dual duct air system.
BranchList,
Dual Duct Air Loop Branches, !- Name
Air Loop Main Branch, !- Branch 1 Name
Heating Coil Air Sys Branch, !- Branch 2 Name
Cooling Coil Air Sys Branch; !- Branch 3 Name
ConnectorList,
Dual Duct Connectors, !- Name
Connector:Splitter, !- Connector 1 Object Type
DualDuctAirSplitter; !- Connector 1 Name
NodeList,
Zone Equipment Inlet Node List, !- Name
Main Hot Air Inlet, !- Node 1 Name
Main Cold Air Inlet; !- Node 2 Name
NodeList,
Air Loop Outlet Node List, !- Name
Heating Coil Outlet Node,!- Node 1 Name
Cooling Coil Outlet Node;!- Node 2 Name
Branch,
Air Loop Main Branch, !- Name
, !- Pressure Drop Curve Name
Fan:ConstantVolume, !- Component 1 Object Type
Supply Fan 1, !- Component 1 Name
Supply Fan Inlet Node, !- Component 1 Inlet Node Name
Supply Fan Outlet Node; !- Component 1 Outlet Node Name
Branch,
Heating Coil Air Sys Branch, !- Name
, !- Pressure Drop Curve Name
Coil:Heating:Water, !- Component 1 Object Type
Main Heating Coil, !- Component 1 Name
Heating Coil Inlet Node, !- Component 1 Inlet Node Name
Heating Coil Outlet Node;!- Component 1 Outlet Node Name
Branch,
Cooling Coil Air Sys Branch, !- Name
, !- Pressure Drop Curve Name
Coil:Cooling:Water, !- Component 1 Object Type
Simple Cooling Coil, !- Component 1 Name
Cooling Coil Inlet Node, !- Component 1 Inlet Node Name
Cooling Coil Outlet Node;!- Component 1 Outlet Node Name
Connector:Splitter,
DualDuctAirSplitter, !- Name
Air Loop Main Branch, !- Inlet Branch Name
Heating Coil Air Sys Branch, !- Outlet Branch 1 Name
Cooling Coil Air Sys Branch; !- Outlet Branch 2 Name
Fan:ConstantVolume,
Supply Fan 1, !- Name
FanAndCoilAvailSched, !- Availability Schedule Name
0.7, !- Fan Efficiency
600.0, !- Pressure Rise {Pa}
autosize, !- Maximum Flow Rate {m3/s}
0.9, !- Motor Efficiency
1.0, !- Motor In Airstream Fraction
Supply Fan Inlet Node, !- Fan Inlet Node Name
Supply Fan Outlet Node; !- Fan Outlet Node Name
Coil:Cooling:Water,
Simple Cooling Coil, !- Name
CoolingCoilAvailSched, !- Availability Schedule Name
autosize, !- Design Water Flow Rate {m3/s}
autosize, !- Design Air Flow Rate {m3/s}
autosize, !- Design Inlet Water Temperature {C}
autosize, !- Design Inlet Air Temperature {C}
autosize, !- Design Outlet Air Temperature {C}
autosize, !- Design Inlet Air Humidity Ratio {kg-H2O/kg-air}
autosize, !- Design Outlet Air Humidity Ratio {kg-H2O/kg-air}
Cooling Coil Water Inlet Node, !- Water Inlet Node Name
Cooling Coil Water Outlet Node, !- Water Outlet Node Name
Cooling Coil Inlet Node, !- Air Inlet Node Name
Cooling Coil Outlet Node,!- Air Outlet Node Name
SimpleAnalysis, !- Type of Analysis
CrossFlow; !- Heat Exchanger Configuration
AirLoopHVAC:ZoneSplitter,
ZoneColdAirSupplySplitter, !- Name
Main Cold Air Inlet, !- Inlet Node Name
Zone 1 Dual Duct Cold Inlet, !- Outlet 1 Node Name
Zone 2 Dual Duct Cold Inlet, !- Outlet 2 Node Name
Zone 3 Dual Duct Cold Inlet; !- Outlet 3 Node Name
AirLoopHVAC:ZoneSplitter,
ZoneHotAirSupplySplitter,!- Name
Main Hot Air Inlet, !- Inlet Node Name
Zone 1 Dual Duct Hot Inlet, !- Outlet 1 Node Name
Zone 2 Dual Duct Hot Inlet, !- Outlet 2 Node Name
Zone 3 Dual Duct Hot Inlet; !- Outlet 3 Node Name
AirLoopHVAC:ZoneMixer,
ZoneReturnAirMixer, !- Name
Return Air Mixer Outlet, !- Outlet Node Name
Zone 1 Outlet Node, !- Inlet 1 Node Name
Zone 2 Outlet Node, !- Inlet 2 Node Name
Zone 3 Outlet Node; !- Inlet 3 Node Name
Coil:Heating:Water,
Main Heating Coil, !- Name
FanAndCoilAvailSched, !- Availability Schedule Name
autosize, !- U-Factor Times Area Value {W/K}
autosize, !- Maximum Water Flow Rate {m3/s}
Heating Coil Water Inlet,!- Water Inlet Node Name
Heating Coil Water Outlet, !- Water Outlet Node Name
Heating Coil Inlet Node, !- Air Inlet Node Name
Heating Coil Outlet Node,!- Air Outlet Node Name
UFactorTimesAreaAndDesignWaterFlowRate, !- Performance Input Method
autosize, !- Nominal Capacity {W}
82.2, !- Design Inlet Water Temperature {C}
16.6, !- Design Inlet Air Temperature {C}
71.1, !- Design Outlet Water Temperature {C}
32.2; !- Design Outlet Air Temperature {C}
Controller:WaterCoil,
Main Cooling Coil Controller, !- Name
Temperature, !- Control Variable
Reverse, !- Action
FLOW, !- Actuator Variable
Cooling Coil Outlet Node,!- Sensor Node Name
Cooling Coil Water Inlet Node, !- Actuator Node Name
0.001, !- Controller Convergence Tolerance {deltaC}
autosize, !- Maximum Actuated Flow {m3/s}
0.0; !- Minimum Actuated Flow {m3/s}
Controller:WaterCoil,
Main Heating Coil Controller, !- Name
Temperature, !- Control Variable
Normal, !- Action
FLOW, !- Actuator Variable
Heating Coil Outlet Node,!- Sensor Node Name
Heating Coil Water Inlet,!- Actuator Node Name
0.01, !- Controller Convergence Tolerance {deltaC}
autosize, !- Maximum Actuated Flow {m3/s}
0.0; !- Minimum Actuated Flow {m3/s}
Obviously, the creation of such a system/plant network description is best handled by a graphical user interface (GUI). However, for testing purposes a developer may have to create the input for a component by hand and insert it into an existing IDF. Then the developer must be careful to choose unique names for the branches and nodes and make sure the entire network makes physical sense.
Branches, Connectors, and Nodes[LINK]
In EnergyPlus, the HVAC system and plant form a network (technically, a graph). The individual pieces of equipment – the fans, coils, chillers, etc. – are connected together by air ducts and fluid pipes. In EnergyPlus nomenclature, the air and fluid circuits are called loops. Specifying how an individual system and plant are connected is done in the EnergyPlus input (IDF) file. The overall structure of the network is defined with Branch and Connector objects. The detail is filled with components and their inlet and outlet nodes. A Branch consists of one or more components arranged sequentially along a pipe or duct. A Connector specifies how three or more branches are connected through a Splitter or Mixer. Nodes connect components along a branch: the outlet node of one component is the inlet node of the next downstream component. The nodes represent conditions at a point on a loop. Each component has one or more inlet and outlet nodes, depending on how many loops it interacts with. A fan, for instance, has one inlet node and one outlet node, since it interacts with a single air loop. A water coil will have 2 inlet and 2 outlet nodes, since it interacts with an air and a fluid loop. Figure 1 shows a diagram of an EnergyPlus HVAC input.
HVAC Input Diagram
As an illustration of how such a network is built up on the IDF, here is the section of the IDF that describes the supply fan, splitter, and heating and cooling coil section of the dual duct air system.
BranchList,
Dual Duct Air Loop Branches, !- Name
Air Loop Main Branch, !- Branch 1 Name
Heating Coil Air Sys Branch, !- Branch 2 Name
Cooling Coil Air Sys Branch; !- Branch 3 Name
ConnectorList,
Dual Duct Connectors, !- Name
Connector:Splitter, !- Connector 1 Object Type
DualDuctAirSplitter; !- Connector 1 Name
NodeList,
Zone Equipment Inlet Node List, !- Name
Main Hot Air Inlet, !- Node 1 Name
Main Cold Air Inlet; !- Node 2 Name
NodeList,
Air Loop Outlet Node List, !- Name
Heating Coil Outlet Node,!- Node 1 Name
Cooling Coil Outlet Node;!- Node 2 Name
Branch,
Air Loop Main Branch, !- Name
, !- Pressure Drop Curve Name
Fan:ConstantVolume, !- Component 1 Object Type
Supply Fan 1, !- Component 1 Name
Supply Fan Inlet Node, !- Component 1 Inlet Node Name
Supply Fan Outlet Node; !- Component 1 Outlet Node Name
Branch,
Heating Coil Air Sys Branch, !- Name
, !- Pressure Drop Curve Name
Coil:Heating:Water, !- Component 1 Object Type
Main Heating Coil, !- Component 1 Name
Heating Coil Inlet Node, !- Component 1 Inlet Node Name
Heating Coil Outlet Node;!- Component 1 Outlet Node Name
Branch,
Cooling Coil Air Sys Branch, !- Name
, !- Pressure Drop Curve Name
Coil:Cooling:Water, !- Component 1 Object Type
Simple Cooling Coil, !- Component 1 Name
Cooling Coil Inlet Node, !- Component 1 Inlet Node Name
Cooling Coil Outlet Node;!- Component 1 Outlet Node Name
Connector:Splitter,
DualDuctAirSplitter, !- Name
Air Loop Main Branch, !- Inlet Branch Name
Heating Coil Air Sys Branch, !- Outlet Branch 1 Name
Cooling Coil Air Sys Branch; !- Outlet Branch 2 Name
Fan:ConstantVolume,
Supply Fan 1, !- Name
FanAndCoilAvailSched, !- Availability Schedule Name
0.7, !- Fan Efficiency
600.0, !- Pressure Rise {Pa}
autosize, !- Maximum Flow Rate {m3/s}
0.9, !- Motor Efficiency
1.0, !- Motor In Airstream Fraction
Supply Fan Inlet Node, !- Fan Inlet Node Name
Supply Fan Outlet Node; !- Fan Outlet Node Name
Coil:Cooling:Water,
Simple Cooling Coil, !- Name
CoolingCoilAvailSched, !- Availability Schedule Name
autosize, !- Design Water Flow Rate {m3/s}
autosize, !- Design Air Flow Rate {m3/s}
autosize, !- Design Inlet Water Temperature {C}
autosize, !- Design Inlet Air Temperature {C}
autosize, !- Design Outlet Air Temperature {C}
autosize, !- Design Inlet Air Humidity Ratio {kg-H2O/kg-air}
autosize, !- Design Outlet Air Humidity Ratio {kg-H2O/kg-air}
Cooling Coil Water Inlet Node, !- Water Inlet Node Name
Cooling Coil Water Outlet Node, !- Water Outlet Node Name
Cooling Coil Inlet Node, !- Air Inlet Node Name
Cooling Coil Outlet Node,!- Air Outlet Node Name
SimpleAnalysis, !- Type of Analysis
CrossFlow; !- Heat Exchanger Configuration
AirLoopHVAC:ZoneSplitter,
ZoneColdAirSupplySplitter, !- Name
Main Cold Air Inlet, !- Inlet Node Name
Zone 1 Dual Duct Cold Inlet, !- Outlet 1 Node Name
Zone 2 Dual Duct Cold Inlet, !- Outlet 2 Node Name
Zone 3 Dual Duct Cold Inlet; !- Outlet 3 Node Name
AirLoopHVAC:ZoneSplitter,
ZoneHotAirSupplySplitter,!- Name
Main Hot Air Inlet, !- Inlet Node Name
Zone 1 Dual Duct Hot Inlet, !- Outlet 1 Node Name
Zone 2 Dual Duct Hot Inlet, !- Outlet 2 Node Name
Zone 3 Dual Duct Hot Inlet; !- Outlet 3 Node Name
AirLoopHVAC:ZoneMixer,
ZoneReturnAirMixer, !- Name
Return Air Mixer Outlet, !- Outlet Node Name
Zone 1 Outlet Node, !- Inlet 1 Node Name
Zone 2 Outlet Node, !- Inlet 2 Node Name
Zone 3 Outlet Node; !- Inlet 3 Node Name
Coil:Heating:Water,
Main Heating Coil, !- Name
FanAndCoilAvailSched, !- Availability Schedule Name
autosize, !- U-Factor Times Area Value {W/K}
autosize, !- Maximum Water Flow Rate {m3/s}
Heating Coil Water Inlet,!- Water Inlet Node Name
Heating Coil Water Outlet, !- Water Outlet Node Name
Heating Coil Inlet Node, !- Air Inlet Node Name
Heating Coil Outlet Node,!- Air Outlet Node Name
UFactorTimesAreaAndDesignWaterFlowRate, !- Performance Input Method
autosize, !- Nominal Capacity {W}
82.2, !- Design Inlet Water Temperature {C}
16.6, !- Design Inlet Air Temperature {C}
71.1, !- Design Outlet Water Temperature {C}
32.2; !- Design Outlet Air Temperature {C}
Controller:WaterCoil,
Main Cooling Coil Controller, !- Name
Temperature, !- Control Variable
Reverse, !- Action
FLOW, !- Actuator Variable
Cooling Coil Outlet Node,!- Sensor Node Name
Cooling Coil Water Inlet Node, !- Actuator Node Name
0.001, !- Controller Convergence Tolerance {deltaC}
autosize, !- Maximum Actuated Flow {m3/s}
0.0; !- Minimum Actuated Flow {m3/s}
Controller:WaterCoil,
Main Heating Coil Controller, !- Name
Temperature, !- Control Variable
Normal, !- Action
FLOW, !- Actuator Variable
Heating Coil Outlet Node,!- Sensor Node Name
Heating Coil Water Inlet,!- Actuator Node Name
0.01, !- Controller Convergence Tolerance {deltaC}
autosize, !- Maximum Actuated Flow {m3/s}
0.0; !- Minimum Actuated Flow {m3/s}
Obviously, the creation of such a system/plant network description is best handled by a graphical user interface (GUI). However, for testing purposes a developer may have to create the input for a component by hand and insert it into an existing IDF. Then the developer must be careful to choose unique names for the branches and nodes and make sure the entire network makes physical sense.
Documentation content copyright © 1996-2022 The Board of Trustees of the University of Illinois and the Regents of the University of California through the Ernest Orlando Lawrence Berkeley National Laboratory. All rights reserved. EnergyPlus is a trademark of the US Department of Energy.
This documentation is made available under the EnergyPlus Open Source License v1.0.